U-value- what's it worth?

Can anyone put a price on U-value?

Take an average size house, with average people, with average heating requirements & using an average fuel- if you reduce the wall U-value by say 0.01- how much will this save in the long run? Basically what I am trying to say is, what is the payback? Does it save £10, £100 or £500 a year? Why spend thousands trying to reduce the U-value if the time taken to recoup that money in terms of fuel savings takes 100 years?

I appreciate there are so many factors to take into account that this could never be accurately worked out. I am also aware that we want to reduce U-value etc to help our planet but to be honest I'd say most people are interested in what money it will save them in the long-run. I also understand that savings will probably increase as the years go by as oil prices etc continue to rise.

Is it worth my while spending 5K extra for extra insulation, aerated blocks, wider cavity etc to reduce U-value by 0.03-0.04? I'd be interested to hear (see) some opinions on this.

as a ber assessor who regularly plays with u values... i can mak eteh following comments...

u vales suffer the law of diminishing marginal returns..
what i mean is, if you drop from 0.25 to 0.23 you save significantly more energy than going from 0.15 to 0.13.... therefor ethe lower the u value the less impact any more reduction will make, and also, the ability to reduce you u value becomes a lot harder when you are down to low levels... and obviously costs increase exponentially...

generally passive house u value levels are in the region of 0.1 - 0.12....

in my opinion you should be looking for an upgrade of about 20% above minimum levels for optimal ecomomy versus efficiency..

roofs try to get around 0.12..
walls 0.2
floors 0.15

what i have noticed in doing ber assessments on new builds is that its the lower cost upgrades that are worth more in teh long run, than trying simply to increase u values...

create a draught lobby at your main access
increase all your heating controls... have many zones with manytime and temp controls
use delayed start stats
use high efficiency boiler
use LELs throughout
use weather and load compensators, especially with UFH

and most importantly, get your construction detail sabsolutely perfect to minimise cold bridges and maximise air tightness... many builders / self builders say "sure thats grand, we always do..."... which is rubbish.... the standards in open systems of irish construction is terrible.

in my opinion you need a BER assessment done with different specifications which should (depending on teh ability of teh assessor) tell you exactly how much energy you save using different specs / materials / construction methods...

Not sure about the monetry value, but put the insulated slab in the kids bedrooms and have to say the rooms are remarkably more comfortable. Used to have to put the heating on mid night but those days are gone now.